Hello,
We have this weird issue since some months and it happened three times now. I made some rules through Winbox like to block Facebook/Youtube in our office through Layer7, and allowed some MAC Addresses to keep the access to Facebook/Youtube.
1st time) The password of router was changed. Many people could access Facebook/Youtube and many can't, especially no one can access whom I have allowed the access to Layer7 rule I created. First time when it happened I thought it's just a one time issue so no worries and I re-setted router with my backup.
2nd time) Again the password of router was changed and same issue as above. Now I also blocked 8291 from remote access. Previously I allowed 8291 access but this time I blocked it, thinking that ISP might be accessing my router through remote connection. I verified that port is blocked through multiple checks.
3rd time) This time password is not changed and I'm sure that password is not with anyone else except me but issue is same as above. When I got to know that one of the person is using Facebook, I immediately accessed my router. Password is not changed, but I see many rules in Filter Rules page which I didn't created myself. As I said 8291 port is blocked. The interesting part is all the names/comment of Rules (those I didn't created) were with the suffix of name of my ISP. So I'm sure they are creating it.

Can anyone tell me if it's possible for ISP to access our router and make changes? Is there any way to stop it? Or according to your expertise what would be causing such issue?

Was the MT supplied by your ISP? If Yes...sure they can. If Not...they won't touch it.
Sure the MT is not compromised by a hacker?

By MT you mean Mikrotik box? Yes they supplied it. So you mean they have some exploit in the device that they could gain access anytime?

If the Mikrotik was supplied by the ISP then it's entirely possible they will give themselves remote access by adding an allow rule in the input chain from their network. We often do this as if we provide a Mikrotik, we tend to also look after it - Most people struggle to open a port on a basic web managed router, they'd have no hope with a Mikrotik so we often do it for them. (But this would be because they'd contacted us to ask us to help them do it)

It's highly unlikely they would be messing with your firewall rules though, or making any changes without you being involved. Also, any remote access would simply be by allowing themselves in the firewall, they wouldn't add any sort of backdoor or exploit. (Unless this is a really dodgy ISP).

What do the rules that are being added look like (and what's currently in your firewall input chain)?

So you mean they have some exploit in the device that they could gain access anytime?

Depending on your software version, yes, that is correct. See https://blog.mikrotik.com/security/winb ... ility.html

Also, it's a good idea to monitor https://blog.mikrotik.com/security/

check if you have ssh enabled and mutiple user with Full Access.

ISP can block your access to facebook / youtube on their part of the network, without having to access your router. Plus, it does not make any sence for them to do this. Remeber ISP is a business, time is money, why spend the time and effort but not get paid ?

you can disalbe port 80, ssh and telnet. and add your own LAN IP to Winbox Service. This is more restrict then the firewall rule make sure you lan IP is static and remember that it is...

You say you restrict access to the machine on the WAN side, but the hacker can be inside your LAN, especially if the result of their activity is only that they permit access to facebook and youtube.

Or in a more sophisticated way, a malware on one of your LAN clients' PCs may connect to your Mikrotik if it had the Winbox service open in the past, without the user of that PC being aware.

So I would

• export (not backup) the configuration into a file
• download the file, analyze and understand the purpose of every single line of it, and remove everything dangerous from it
• netinstall the mikrotik (upgrade is not enough) with 6.43.2 or at least 6.42.9
• create the users and set to all of them different passwords than they had ever before
• upload the sanitized configuration file to the netinstalled Mikrotik, named e.g. clean-cfg.rsc
• use /system reset-configuration run-after-reset=clean-cfg.rsc to restore the previous configuration from the sanitized export

Netinstall will invalidate all your certificates if any, but that's the price to pay unfortunately.

To further increase security, you can disable http, telnet, api and Winbox completely (even for access from LAN) and permit only https access (which requires to create a certificate) and/or ssh access.

In any case, the ISP is the least likely source of the issue.

That's what happens when you put restrictions on people: Le Chatelier's principle. The system changes to escape the constrain.
I would look for the "hacker" on the inside. But if they are your employees, this could rather trigger personnel fluctuations instead of increased productivity.